Thursday, 24 May 2012

Skylab

Skylab was the first space station the United States launched into
orbit, and the second space station ever visited by a human crew. The 75
metric ton station was in Earth orbit from 1973 to 1979, and it was
visited by crews three times in 1973 and 1974. It included a laboratory
for studying the effects of microgravity and a solar observatory.Skylab was launched 14 May 1973 by a Saturn INT-21 (a two-stage
version of the Saturn V launch vehicle) into a 235 nautical mile (435
km) orbit. The launch is sometimes referred to as Skylab 1, or SL-1.
Severe damage was sustained during launch, including the loss of the
station's micro meteoroid shield/sun shade and one of its main solar
panels. Debris from the lost micro meteoroid shield further complicated
matters by pinning the remaining solar panel to the side of the station,
preventing its deployment and thus leaving the station with a huge
power deficit. The station underwent extensive repair during a spacewalk
by the first crew, which launched on 25 May 1973 (the SL-2 mission)
atop a Saturn IB. Two additional missions followed on 28 July 1973
(SL-3) and 16 November 1973 (SL-4) with stay times of 28, 59, and 84
days, respectively. The last Skylab crew returned to Earth on 8 February
1974.
Skylab orbited Earth 2,476 times during the 171 days and 13 hours of
its occupation during the three manned Skylab missions. Astronauts
performed ten spacewalks totalling 42 hours 16 minutes. Skylab logged
about 2,000 hours of scientific and medical experiments, including eight
solar experiments. The Sun's coronal holes were discovered thanks to
these efforts. Many of the experiments conducted investigated the
astronauts' adaptation to extended periods of microgravity. Each Skylab
mission set a record for the amount of time astronauts spent in space.
Following the last mission, Skylab was left in a parking orbit
expected to last at least eight years. The Space Shuttle was planned to
dock with and elevate Skylab to a higher safe altitude in 1979; however,
the shuttles were not able to launch until 1981. A planned unmanned
satellite called the Teleoperator was to be launched to save Skylab, but
funding never materialized. Skylab was in need of a major overhaul,
including new gyroscopes, and was low on fuel. Some systems were not
designed for maintenance in space; however this type of problem had been
overcome before such as when the primary coolant loop was repaired.
Increased solar activity, heating the outer layers of the Earth's
atmosphere and thereby increasing drag on Skylab, led to an early
reentry at approximately 16:37 UTC 11 July 1979. In the weeks leading up
to the reentry, ground controllers had re-established contact with the
six year old vehicle, and were able to adjust its attitude for optimal
reentry dynamics. Earth reentry footprint was a narrow band (approx. 4�
wide) beginning at about 48� S 87� E and ending at about 12� S 144� E,
an area covering portions of the Indian Ocean and Western Australia.
Debris was found between Esperance, Western Australia, and Rawlinna,
Western Australia, 31�34�S, 122�126�E.